With growing demand for more efficient energy supplies, energy storage systems such as batteries and capacitors with higher energy and power densities are needed for powering vehicles and the like. Lithium ion batteries (LIBs) for example, are one of the most widely used portable power sources, and they have been instrumental in the development of more fuel-efficient vehicles, such as electric vehicles (EV) and hybrid electrical vehicles (HEV). However, loss of power and capacity upon storage or prolonged use especially at elevated temperature limits the application of LIBs for EV and HEY applications. Thus, there is a need to have Lithium-ion batteries with a higher energy density, higher power density, longer cycle life, longer calendar life, lower cost.
It is recognized that these devices may be improved by replacing graphite with silicon. Silicon has the potential to replace graphite as the active anode material in secondary lithium-ion electrochemical cells. The theoretical capacity of silicon is superior to that of graphite (4,200 mAh/g(si) vs. 373 mAh/g(c)) assuming discharged products in the forms of Li4.4Si and LiC6. However, current attempts to replace graphite with silicon or silicon-based materials have failed to meet cycle life requirements due to the volume expansion associated with lithiation of silicon material (Si→Li4.4Si) and first cycle irreversible capacity loss.
These issues are not limited to Si-based anodes but are also associated with Sn-based anodes. To a much lesser extent, the volume expansion issue is also limiting the performance of cathodes in batteries with various types of cell chemistries. Some approaches to resolve the problems of Si-based anodes are the use of binding materials, such as PVDF, and making the powder material small, core-shell architectures that cover the silicon particles with carbon and evaporated thin films of silicon on nickel materials. It is desired to have an electrode morphology and architecture for energy storage devices as mentioned above, that increases the rate of charge/discharge, battery life, and decreases cost, and in particular, silicon architecture that avoids or minimizes volume expansion and related issues.